Cavity resonator electronic oscillation generator



1952 J. H. FREMLIN ET AL 2,513,335

CAVITY RESONATOR ELECTRONIC OSCILLATION GENERATOR Filed Oct. 28, 1942' 3 Sheets-Sheet l I nventog's J.H,F smLu/ w- Hill- Attorney Oct. 7, 1952 J. H. FREMLIN ET AL 2,

CAVITY RESONATOR ELECTRONIC OSCILLATION GENERATOR Filed Oct. 28, 1942 s Sheets-Sheet 2 F/G. /O.

J H r fim I 2/ I H8114.

A ltorney 2,613,335 CAVITY RESONATOR ELECTRONIC OSCILLATION GENERATOR Filed Oct. 28, 1942 Oct. 7, 1952 J. H. FREMLIN ET AL 3 Sheets-Sheet 5 Patented Oct. 7, 1952 i TY"RESNA i'Ei G O OS'CIELATION GENERATOR? Johns? Beaver-*Fremlin and Roger Norman flail, I

London England assignors by mesrie V assignments to International Standard "Electric (301 pnratiom, New. York, N.

Delaware Y.,' a "corporation or ApflIicatioiiJOctiiberIZS,'1942, Serial No. 463,699 InztGmeat Bi-itain December-.112; 1941 The Presentinventiomrelatestto arrangements for producing an electron beam particularly for electron t discharge deviceseomprisinghigh frequencyresonant chambers; I

in oscillators of? the .velocityi modulation type for; very short wavelengths-itisr in general desirable totuse electron str'eamslof veryjhigh 'currentdensity, 'I'his. .-follows at once: from; the fact that for atgiven beam voltage the mechani.-. cal dimensionsdof the tcircuit are redueedtas vthe wavelength isreducedand consequently a vsmaller cross'sectionaltarea;.of .beam mustheuused. This meansv that inn order that an adequate power output should be obtained-either voltagefor. curlrent density must helincreasedt An object. or this invention. is to; provide arrangements for. producing; electronubeamsfl in which very large current densities may beobtained and: are usedto produce oscillations? This isinrgeneral accomplishedJoy, employing a i substantially uniform magnetic field having lines .of .fmagnetic force. substantially p'arallelkto an electron; emittingtfsurface, arrangedltodfiect electrons. laterally} into; a; pathigenerally' parallel to; the Surface. in; which". thei-electrorisl are. concentrated toQproduce' the fdes'iredteurfiit .d'nsirties. A further Ohjt'. of" theiihi eht ififi isQto utilize the. electrdiis Said path "fdffiibdilc'e oscmauqns iniresenatcr, and articularly to Obtain this result byj vlocityffiiddiflafiioh."

A further object isto" provide aniarrangemerit The invention wnrrbefurtnert des'crib'ed with reference to the. accompan ing drawings in which Fig.1 is a; d'ittgralin' to show the theory, of the invention. i

Fig. 3"is"agraph to-sho'w variation u'of' current density; with" dist'ar'ieefrdm the cat ode in arrangements. according to; the" Invention;

FigSI 4', '5; 6 and alfi diagrammatic d'rEWiiTgiS' shdwm'gr constructions" according: t0 :1 the iiiven-tion."- I

. Fig; 8 is L an enlarged view of. part of; 7 showing two lines of forcel ligs. 9t and) 10 show diacrammatieallylt. two

In 1,valp1ane emitting surface I is illu's- N ofithe arrow A at thepointTis *very large;- C'Ollfl pared tothe; emission" density 'at' the cathode surface; all the emission-hetweerrthepointst and" 8:" being concentratedbetween the two lines 8" ans '9? I An ap lication of" this large current csoiic'efi nation may-be made *in the design of ultra high frequency oscillators and power' amplifiers; particularly though not solely'-* of thevelocity-'- iriddu-latien types. It-' may be riotdhere that the eifect or f iill' space charge" limitation has been consideredandis found actually to-be ed vantag'ous to the current concentration desired. in Fl $12 are shown electron-paths whichcan be obtained in) such conditions;

Arrangements according to" the invention for producing electron current concentrations have a. particular advantageiin that the concentrated beam of electrons is produced only after the electrons haveatt'ained acdiisiderable velocity. Spacechar'ge' limitation of the cathode emission does not-therefore r'nakeit necessaryto use've'ry high voltages of very close spacingsof'the e1'ec-'- trodes as is the-case manyknown constructions for theproductionof concentratedbeams. lt iscle'ar from Fig". 2 -thatat the plane 'A- A where-' the electron" velocity is smalland space chargeeffects might be serious; the current density is low" while at B*"B thecurrentdns'ity is much increased and the velecity of the elec tronisals'o lar:

The 'v'ariaticinof current density i with the distenceztfrom the-canteens shown iir'Fig: 3 for space'ichargene'glieible (curve I): andtsp'ace ch'argeliinited (curve 2), 2'0 being'rthe emission density;

Electron beam producing arrangeme'nts,v accordinglto the invention, as already'inferred, are particularly adaptable for incorporation in oscihlators for use at very short wavelengths, of the order of 3 cm. or less. In such oscillators resonant circuits of the types usually used at longer wavelengths become very small. In consequence of this, the amount of electron current which can be used also becomes small. In order to obtain high powers, therefore, it is important to use systems in which the useable cathode area is as great as possible when measured in terms of v, (A is the wave length) Since circuit losses tend to become serious at such short wavelengths, it is also important that circuits should be designed to give the highest possible impedance at the point or points traversed by the driving electron stream, and that the current density in this stream should be as great as possible.

An embodiment of the invention about to be described satisfies all these requirements and is 4 I5 and I6, which are shown more clearly in the enlarged drawing Fig. 8, lose considerable amounts of their D. C. energy and are collected by the anode; one, namely ll suffers little energy change and returns gently to the cathode, and the other [3 gains energy from the H. F. field and returns with it to the cathode.

The magnetic field will not in fact be so critical as might be suggested by the discussion above as an increase, although removing the electrons v slightly from the strongest field, will only allow in many ways an appreciable advance on existing circuit designs for such high frequencies.

Figs. 4-8 show embodiments employing a single high frequency resonant chamber. The chamber in Fig. 4 has a single gap oraperture whilst in Figs. 5-8 the chamber has aplurality of apertures arranged around the circumference of the chamber Referring to Figs. 5-8a cross section of an electron discharge device embodying the invention is shown, the dotted lines showin the tracks of a few typical electron paths. The structure consists of a large cylindrical cathode I, coated on the inner side and containing within it a segmented anode consisting of a series of strip'sB of a cylinder coaxial with l. A magnetic field is applied parallel to the axis of the cylinders. The tracks H, [2, l3, Fig. 5 show the form of path traversed by a series of electrons leaving I in the absence of oscillation, and show. how the whole of the emission from a considerable area of I will be concentrated into a current of very high'density passing closely across the gap between two of the strips B as long as the potential difference between i and B is suitably matched to the magnetic field employed.

Now, oscillations may be set up in the gapsbetween the strips B of a type characterized by the electric force lines, the instantaneous distribution vof which is shown at 14, Fig. 6. It will be noted that an even number of the strips 13 should be used. The wavelength will be very short; if n strips are used, it will be of the order and will be independent of the length of the system perpendicular to the paper. r is the radius of the cylinder on which strips B lie. Energy will be abstracted from the electron stream as it crosses the gaps, thetransfer of energy being a maximum when the electrons remain in the field of the gap for about 1.2 cycles of the oscillation. Now examination of the behavior of theelectrons when oscillation takes place shows that the efiiciency of operation will be at least double that of a diode using the same mechanism of excitation with an electron beam, i. e. of the order of 40%. This is due to the fact that only electrons which have lost kinetic energy, and thus contributed to the maintenance of the oscillation, will be col-'- lected by the strips B if the magnetic field is properly adjusted. Others will return to theoathode and will not, therefore, absorb any D. C.en'ergy. Four typical electron tracks l5l8 are shown in Fig. 7 corresponding to electrons which have left the cathode at intervals of cycle. Two, namely electrons which have lost a useful amount of energy to' reach the anode.

If very high voltages are used, the extremely high emission available might make dissipation of the energy at theanode a serious difiiculty on continuous wave operation, but the system will still be extremely suitable for use as a pulsed generator, and for a given desired power output, the large dimensions of the system compared with the wavelength will allow the dissipation to be spread over a large area.

The oscillating system may, of course take forms other than the cylindrical strips B. For instance, straight fiat strips of, for example; tungsten sheet could equally well be used, the dimensions being appropriately adjusted, or any other sectional form giving suitable gaps when they can be reached by the electron stream with large high frequency fields imposed across themi;

The strips may be mounted on radial supports from the centre of the cylinder formed by strips B or they may be supported in any suitable insulating material, and the frequency may be adjusted within reasonable limits either by any convenient distortion of the system so built up or by the movement of a conductor near the end of the system.

The power generated may be withdrawn in known manner by a probe near the end of the system in'the manner shown in Fig. 12, or by any other well-known method, the output preferably being brought through the vacuum envelope by a suitable wave guide to avoid unnecessary losses.

The lengths of thestrips perpendicular to the section shown in the figures are not important except insofar as it is desirable that they should not be such as to cause resonances at wavelengths which could readily be excited in the same range of voltage and magnetic field.

In Fig. 9 two high'frequency resonant chambers 24, 25 are used as in a now well known klystron circuit and may be coupled externally if the arrangement is to be used as an oscillator. Figs. l1 and 12 show a constructional form of tube according to Fig. 9. The two cavities 26 and 25 are formed in a block 26 of copper, which is however, preferably formed of a series 26' of superposed plates in the manner described in co-pending application Serial No. 457,789.

This block 26 (or superposed plates 26') is placed within a copper cylinder 28 having top and bottom plates 29 of magnetic material. Above and below the block 26 are copper plates'2l to support the block 26 centrally of the height of the cylinder. Plates 30 of mica or similar insulating material support a copper plate 31 at a suitabledistance from the cavities 24, 25. Supported on a portion of the copper plate 3! with the intervention ofinsulation 32 is a cathode l. A coaxial line connector 32 is sealed through a glass bead 34 in turn sealed through the 'cylindrical wall 28 and the inner conductor 33 thereof just protrudes into the cavity 25. Lead'in wires 35 for the cathode heater are sealed through the'; wall:.2.8:,by meanszof:axglasszrbead; The-wall 28 and top.:and-;:bottom.plates-19am:welded:.to gether. or; otherwise joined. in. a vacuum. tight manner; and :thewholewessel is evacuated. A horse shoe magnet ,36; serves; to: support: the vessel by magnetic attraction, and to provide the necessary. magneticzfieldlwithin the..vessel.

Theoperation; Oil the. device will be clear from theedescription given above: Asuitableipotential diff erence, is applied between the. outer. cylinder. 28..and;the cathode; l. Electrons.emittedcbytthe cathodavl areattractedtowards-the .block 2 6 and their paths .are .bentby themagnetic. field .so. that they: followwpaths .shown. in {Fig 9. The electron beam: in passing thecavity 24-is .velocity-modulatest. and whenzpassingzithe portion ofitheblock 26 between cavity '2 4::andcavity "2.5. the; electrons are bunched. When therbunched electrons: pass the; cavity 25 they givelup renergy tothe high free quency; field; within: the. cavity." The; resonant cavities 24 and 25 are closely coupled without the introduction of any specialcoupling.devices. and oscillations of nearly 1 the same-amplitude and ofzthe. same or; opposite phase inthe two cavities 2.4,: 25 are maintained;by thexbeam. There is a series of discrete beam velocities for whicha maximumoccursin the hightfreqnency energy. transferred; fromzthes beam; giving a series of possible operatingvoltages; FigslOshows the invention embodiedin an arrangement using. secondary electron emission amplification and. serving as an oscillatorror; power; amplifier;

It is;:no.t necessary. in: the embodiment shown in1.F.ig: 10 thatsthe modulating and. output. circuits; e: gcl Sand-.20 should beat the same potential; it.may be..advantageous to have the output circuit at-a' highenpotential, the electrodes, ofxcourse, being so disposed as to give suitable electron paths...

Thesecondaryelectron emitting surface 2! is asshown so'arranged as toreceive the electrons returning: towards the first emitting'surface l. On'impact with the surface 2.1, theprimary electrons falling: thereon, cause secondary electrons to be emittedandthe stream 2310i electronsfrom 21 is condensedgin the'same manner as already described. The. primary electron stream 22 is modulatedin intensityby the high frequency field across the aperture of resonantchamber l9. This modulated stream 22 produces an amplified modulated stream ofelectrons-N which excites the resonant; chamber 20 as: they pass across the aperture therein in accordance with the modulation.

What-is claimed is:

1. An electron discharge dey-icevcomprising a cathode havinga substantially. cylindrical electron emitting surface, a tubular anode located concentrically within the cathode surface and having a plurality of openings each communicating with a cavity operating as a cavity resonator-locatedwithin the anode, means for producing a potential difference between thecathodezandanode, meansfor maintaininga magneticfi'eld in thespace between the anode and the cathode surface having lines of magnetic forceparallel to-theaxis ofthe anode and an intensity 'atwhich electrons'emitted at said cathode surface are deflected into arcuate paths passing: adjacent to said openings; and means for extracting high frequency energy from at least one cavity resonator.

2. An" electron discharge-device. with a means for" producing "a concentrated electron beam .comprising acavity-resonator,-- a wall of said resona- 6 tOP'DIOVidBd? with an: opening through whiclr-tlie oscillatingfieldi of theireson-ator can '-extend a cathode having an electron emitting surf-ace of substantial length .inone direction opposite-and equidistant from the resonator wall, means connected to said resonatoryand said cathode for producing a potential. difference' therebetween, and meanstadja-cent said'cathode and saidresonator' for maintaininga magnetic :fiel-d there-1 between, the field having lines: of force perpendicular to said. direction of the. length thereof and an. intensity adapted to deflectrel-ectrons emitted along the-length of: said surfaceinarcu ate paths having a substantial portionequidisa tant from the resonator wall adjacent the open-a ing and concentrated across the opening...

3. A.-devi-ce according to claim: 2 in whichcthe. cathode. surface is tubular;v and-the anod-e suitface is symmetrically arranged around 1 the axis. of. the cathode surfacewithinthecathode.

4; A.-device according: touclaim2 iniwhich the arcuate electron path extendsbacktothe-cathode.

5. An electron-discharge device with-meansior producing a concentrated electron. beam: comprising a cavity resonator, awall of said. resonator provided with an opening through which the oscillating fieldof the resonator can extend, acathode adjacent to andlia-cing the -opening,- an electron emitting surface of substantial. length in one direction on said-cathode equidistant from the resonator wall, means connected to said reso-. nator and said cathode for producing aapotential difference therebetween, and means adjacentisai'd cathode and said resonator for maintaining a magnetic field therebetween, the field having lines of force parallel to. said emitting surface and perpendicular to said direction of the length thereof and an intensity. adapted to deflect electrons emitted along the length of the surface in arcuate paths having a: substantial portion equidistant from the resonator wall adjacent the opening and concentrated. across: the opening in the resonator wall and terminating in the cathode.

6. An electron discharge device with'meansfor producing a concentrated electron beam comprising an anode with a cavity resonator therein; aflat wall of said anode being providedwith an opening through which the oscillating field of the resonator can extend, a flat-cathode parallel to said wall with the opening, anelectr-on emitting surface of substantial length in one direction on said cathode, means connected to said anode and cathode for producing .a potential diffcrence therebetween, and means adjacent said anode-and cathode for maintaining a'magnetic field therebetween, the field having lines of force parallel to said emitting surface and perpendicularto said direction of the length thereofand an intensity adapted to deflect electrons-emitted along the length of said surface in arcuate paths having a portion substantially parallel to said anode wall and concentrated across the opening and terminating in said cathode.

7; An electron discharge device for sustaining ultra high frequency oscillations comprisingtwo cavity resonators each having a .wall with an opening through which the oscillating fields of the-resonators can extend; a cathode having an electron emitting surface of substantial length in one direction, said cathode beingoppositeand equidistant from the resonatorwalls having said openings, means" connected between said reso= natorsand-said cathode'torpr-oducing" apotential difference therebetween, and means adjacent said device for maintaining a magnetic field between said resonators and said cathode, the field having lines of force parallel to said emitting surface and perpendicular to the length thereof and an intensity adapted to deflect electrons emitted along the length of said surface in armate paths having a portion substantially parallel to said resonator walls adjacent the openings in succession and concentrated across the openings.

'8. An electron discharge device for sustaining ultra high frequency oscillations comprising a first and second cavity resonator each having a fiat wall with an opening through which the oscillating fields of the resonators can extend, said walls being aligned and said openings being adjacent each other, a fiat cathode parallel to said aligned resonator walls, an electron emitting surface of substantial length in a direction parallel to said openings and mounted on said cathode, means connected to said cathode and said resonators for producing a potential difference therebetween, means adjacent said device for maintaining a magnetic field between said cathode and said resonators, the field having lines of force perpendicular to the length thereof and an intensity adapted to deflect electrons emitted along the length of said surface in arcuate paths having a portion substantially parallel to said aligned walls, and concentrated across said openings in succession and terminating in said cathode whereby the electrons are velocity modulated in the field of the first resonator and transmit energy to the field of the second resonator, and

means coupled to said second resonator for extracting high frequency oscillations.

9. An electron discharge device with means for producing a concentrated electron beam comprising a first and second cavity resonator, one wall of each said resonator being provided with an opening through which the oscillating field of the resonator can extend, a first and a second cathode mount-ed adjacent said wall of the first and second resonators respectively and having electron emitting surfaces of substantial length in one direction, means connected between said resonators and said cathode for producing a po ential difference therebetween, and means adjacent the space between said resonator and cathodes for producing a magnetic field therebetween, the field having lines of force parallel to said emitting surfaces and perpendicular to said direction of the length thereof and an in-- tensity adapted to deflect electrons emitted along the length of the emitting surface of said first cathode in arcuate paths each having a substantial portion equidistant from the wall of said first resonator, concentrated across the opening therein, and terminating in the emitting surface of said second cathode, said resonator walls being adjacent each other whereby the electrons in said paths are velocity modulated by the first resonator field and electrons are secondarily emitted from said second cathode past said second resonat-cr opening.

10. An electron discharge device according to claim 9 in which the resonator walls are flat and in a comm-on plane substantially, and said emitting surfaces are fiat and parallel to said common plane, the magnetic field intensity being adapted to deflect the electrons secondarily emitted along the length of said second cathode in arcuate paths having a substantial portion equidistant from the wall of the second resonator and concentrated across the opening therein,

whereby the secondarily emitted electrons give up energy to the second resonator field.

11. An electron discharge device with means for producing a concentrated electron beam comprising a cylindrical cathode having an electron emitting surface on the interior thereof, a tubular anode mounted concentrically inside said cathode, said anode having a cavity resonator therein and being provided with openings communicating with said resonator, means connected between said cathode and anode for producing a potential difference therebetween, and means adjacent the space between the cathode and anode for maintaining a magnetic field therein, the field having lines of force parallel to the axis of said cylindrical cathode and an intensity adapted to deflect electrons emitted from said cathode surface in arcuate paths having a substantial portion tangential to the anode surface and concentrated across the openings to said resonator.

1-2. A device according to claim 11 in which the anode comprises a plurality of strips parallel to the axis of the cathode surface and having narrow spaces between the strips forming said openings.

13. An electron discharge device having an envelope enclosing an anode structure having a generally planar surface and provided with a series of mutually spaced slots in said surface dividing the structure into separate anode elements, each of said slots forming a resonant system interconnecting two adjacent anode elements, a cathode structure including a generally planar member mounted in opposed substantially parallel relation to said planar surface of said anode structure and means for providing elec trons in proximity to the said anode elements, means for maintaining said anode structure at a positive unidirectional electric potential with respect to said member for maintaining therebetween a unidirectional electric field substantially normal to said planar surface and said member, and means for producing a magnetic field'parallel to said slots in the space between said anode and cathode structures whereby said anode structure may be set into high frequency resonance as a consequence of the resultant motion of electrons traversing said space.

The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,617,177 Smith Feb. 8, 1927 1,714,406 Smith May 21, 1929 1,720,824 Donle July 16, 1929 2,063,342 Samuel Dec. 8, 1936 2,096,817 Malter Oct. 26, 1937 2,103,362 Hansell Dec. 28, 1937 2,272,165 Varian et a1 Feb. 3, 1942 2,289,220 Smith July 7, 1942 2,320,860 Fremlin 1 June 1, 1943 2,414,121 Pierce Jan. 14, 1947 2,428,612 Blew-ett Oct. 7, 1947 FOREIGN PATENTS Number Country Date 215,600 Switzerland Oct. 16, 1941 509,102 Great Britain July 1'1, 1939 

